Transformer assembly for a magnetic resonance imaging system

ABSTRACT

A transformer assembly includes a substrate having a first surface and an opposing second surface, a first spiral wound inductive coil formed on the first surface, and a second spiral wound inductive coil formed on the first surface; the first and second spiral wound inductive coils forming a double spiral arrangement on the first surface such that the first coil is inductively coupled to the second coil. An RF coil including the transformer assembly and a method of fabricating the transformer assembly are also described.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates generally to radio frequency(RF) coils, and more particularly to a transformer assembly used in anRF coil.

Magnetic Resonance Imaging (MRI) systems use RF coils to acquire imageinformation of a region of interest of a scanned object. The resultantimage that is generated shows the structure and function of the regionof interest. At least one conventional MRI imaging system includes amultiple-channel array coil having a plurality of coil elements. Thesignals detected by the multiple-channel array coil are processed by acomputer to generate MR images of the object being imaged. Duringoperation, the plurality of coil elements are inductively orcapacitively decoupled from the other coil elements. In the majority ofthe cases the inductive decoupling through overlapping is preferred.When overlapping between elements is not possible, the remoteoverlapping is performed. Because the setup resembles the classicaltransformer, the technique of remote inductive decoupling is also calledthe transformer decoupling. Accordingly, the conventional coil elementsare decoupled from one another along a first direction using atransformer decoupling technique. Moreover, the coil elements aredecoupled from one another along a second direction using a preamplifierdecoupling technique.

The transformer decoupling technique utilizes a conventional transformerthat is disposed between each pair of coil elements. The conventionaltransformer includes a pair of inductor coils that are wound around acylindrical dielectric. In operation, the mutual inductance of thetransformer inductors may have both a positive and a negative effect onthe coil elements based on the reciprocal current directions in the coilelements. For example, when the coil element fluxes add up, or have samedirection, then the mutual inductance is positive. However, when thecurrent directions are opposed to each other, then the mutual inductanceis negative. A positive mutual inductance is typically desired forunder-lapped coil elements and a negative inductance is typicallydesired for overlapped coil elements.

However, inserting the conventional transformer between a pair of coilelements results in an additional inductance being added to theinductance of the coil elements. The additional inductance requires thecoil elements to be retuned. Additionally, coupling adjustment of theconventional transformer is difficult. More specifically, thetransformer inductors are stretched or compressed to achieve the desiredinductance. After the inductor has been formed into a final state, theinductor is coated with a substance to maintain the inductor in thefinal state. Thus, the conventional transformers are not easily modifiedto alter the decoupling inductance.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one embodiment, a transformer assembly is provided.The transformer assembly includes a substrate having a first surface andan opposing second surface, a first spiral wound inductive coil formedon the first surface, and a second spiral wound inductive coil formed onthe first surface; the first and second spiral wound inductive coilsforming a double spiral arrangement on the first surface such that thefirst coil is inductively coupled to the second coil.

In another embodiment, a multiple channel array coil for magneticresonance imaging is provided. The array coil includes a first coil, asecond coil, and a transformer coupled between the first and secondcoils. The transformer includes a substrate having a first surface andan opposing second surface, a first spiral wound inductive coil formedon the first surface, and a second spiral wound inductive coil formed onthe first surface; the first and second spiral wound inductive coilsforming a double spiral arrangement on the first surface such that thefirst coil is inductively coupled to the second coil.

In a further embodiment, a method of fabricating a transformer assemblyis provided. The method includes forming a first spiral electricalinductor on a first surface of a dielectric substrate, and forming asecond spiral electrical inductor on the first surface of the substratesuch that the first spiral inductor is interleaved with the secondspiral inductor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary multiple channelarray coil formed in accordance with various embodiments.

FIG. 2 is a top view of an exemplary transformer assembly formed inaccordance with various embodiments.

FIG. 3 is a bottom view of the exemplary transformer assembly shown inFIG. 2.

FIG. 4 is a side view of a portion of the transformer assembly shown inFIGS. 2 and 3.

FIG. 5 is another side view of a portion of the transformer assemblyshown in FIGS. 2 and 3.

FIG. 6 is a flowchart of an exemplary method of fabricating an inductorassembly in accordance with various embodiments.

FIG. 7 is a pictorial view of an exemplary medical imaging system thatmay be utilized with an exemplary inductor assembly formed in accordancewith various embodiments.

FIG. 8 is a simplified schematic illustration of the medical imagingsystem shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofcertain embodiments, will be better understood when read in conjunctionwith the appended drawings. To the extent that the figures illustratediagrams of the functional blocks of various embodiments, the functionalblocks are not necessarily indicative of the division between hardwarecircuitry. Thus, for example, one or more of the functional blocks(e.g., processors, controllers or memories) may be implemented in asingle piece of hardware (e.g., a general purpose signal processor orrandom access memory, hard disk, or the like) or multiple pieces ofhardware. Similarly, the programs may be stand alone programs, may beincorporated as subroutines in an operating system, may be functions inan installed software package, and the like. It should be understoodthat the various embodiments are not limited to the arrangements andinstrumentality shown in the drawings.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features. Moreover, unless explicitlystated to the contrary, embodiments “comprising” or “having” an elementor a plurality of elements having a particular property may includeadditional such elements not having that property.

Various embodiments described herein provide a transformer assembly thatmay be utilized with a multi-channel radio-frequency (RF) coil assembly.By practicing at least one embodiment, the transformer assemblydescribed herein may be tuned prior to being installed in the MRIsystem, thus reducing labor costs associated with installation andtuning. The transformer assembly may be implemented in connection withdifferent types of magnetic resonance coils, for example surface coils,operating at different frequencies, thus having different wavelengths.

FIG. 1 is a schematic illustration of an exemplary multiple channelarray coil assembly 10 formed in accordance various embodiments. Thearray coil assembly 10 includes a left portion 12 and a right portion 14as illustrated in FIG. 1. The left and right portions 12 and 14 aresymmetrically arranged with one another and displaced from one anotherwith respect to an x-axis. Each of the left and right portions 12 and 14include a pair of individual, overlapping surface coil elements that arearranged along a y-axis. For example, the left portion 12 includes twogenerally rectangular, coil elements 20 and 22. Moreover, the rightportion 14 includes two, generally rectangular, coil elements 24 and 26.In the exemplary embodiment, the coil elements 20, 22, 24 and 26 aregenerally rectangular in shape, and are formed from a generally flat,conductive material, for example, tin-plated copper. It should berealized that the multiple channel array coil assembly 10 may be usedwith other multiple channel array coils (not shown). For example, thearray coil assembly 10 may be used to image a posterior section of apatient, whereas another array coil (not shown) may be disposed over orunder the array coil assembly 10 to image an anterior portion of thepatient.

In operation, the coil elements 20, 22, 24 and 26 are preferablyphysically separated from each other by, in some embodiments,overlapping the coil elements such that the coils 20, 22, 24 and 26 eachgenerate a distinct sensitivity profile. For example, in thisembodiment, the coil elements 20 and 24 are overlapped with the coilelements 22 and 26, respectively. As shown in FIG. 1, a portion of thecoil elements 20 and 22 are inwardly bent at an angle of approximately45 degrees from both sides, thereby resulting in two intersection points30 and 32 such that the coil elements 20 and 22 overlap and intersect ata generally perpendicular angle with respect to one another. Moreover, aportion of the coil elements 24 and 26 are inwardly bent at an angle ofapproximately 45 degrees from both sides, thereby resulting in twointersection points 34 and 36 such that the coil elements 24 and 26overlap and intersect at a generally perpendicular angle with respect toone another.

In the exemplary embodiment, the individual coil elements 20, 22, 24 and26 are decoupled from one another along the x-direction using atransformer decoupling method. Accordingly, the array coil assembly 10also includes a first transformer 40 that is coupled between the coilelements 20 and 24 and a second transformer 42 that is coupled betweenthe coil elements 22 and 26. Moreover, the elements 20, 22, 24 and 26are decoupled from one another along the y-direction using preamplifierdecoupling. Accordingly, the array coil assembly 10 also includes apreamplifier 44 that is coupled to the coil element 20, a preamplifier46 that is coupled to the coil element 22, a preamplifier 48 that iscoupled to the coil element 24, and a preamplifier 50 that is coupled tothe coil element 26. In the exemplary embodiment, the array coilassembly 10 also includes a plurality of capacitors (shown in FIG. 2).The operation and location of the capacitors is discussed in more detailbelow. However, it should be noted that other suitable overlapping andnon-overlapping arrangements may be used.

FIG. 2 is a top view of an exemplary tunable adjustable transformerassembly 100 that may be used with the array coil assembly 10 shown inFIG. 1 in accordance with various embodiments. FIG. 3 is a bottom viewof the exemplary transformer assembly 100 shown in FIG. 2. It should benoted, that in the exemplary embodiment, the transformer assembly 100may be installed in the multiple channel array coil assembly 10 shown inFIG. 1 in lieu of the transformer 40.

In the exemplary embodiment, the transformer assembly 100 includes asubstrate 102 having a first surface 104 and an opposing second surface106. The substrate 102 is fabricated using a dielectric material suchas, for example FR4. FR4 is dielectric material that may be, forexample, a fiberglass reinforced epoxy laminate that is flame retardant(FR) and self-extinguishing. In the exemplary embodiment, the firstsurface 104 is substantially planar or flat and the second opposingsurface is also substantially planar or flat. Moreover, the firstsurface 104 is substantially parallel with the second surface 106.

The transformer assembly 100 also includes a first spiral inductor 110and a second spiral inductor 112. As shown in FIG. 2, the first spiralinductor 110 includes a first inductor portion 120 that is formed on thefirst surface 104 of the substrate 102 and a second inductor portion 122(shown in FIG. 3) that is formed on the second surface 106 of thesubstrate 102. The second spiral inductor 112 includes a first inductorportion 124 (shown in FIG. 2) that is formed on the first surface 104 ofthe substrate 102 and a second inductor portion 126 (shown in FIG. 3)that is formed on the second surface 106 of the substrate 102. In theexemplary embodiment, the first and second portions 120 and 124 and 122and 126 are rigidly formed on the substrate 102 using, for example, avapor chemical deposition procedure.

In the exemplary embodiment, the first inductor portion 120 issubstantially symmetrical with the second inductor portion 122. Morespecifically, the spiral portion of the first inductor portion 120 hassubstantially the same size, shape, and relative orientation as thespiral portion of the second inductor portion 122, but is disposed on anopposite side of the substrate 102. It should be realized that althoughthe spiral portions of the first and second inductor portions 120 and122 are substantially similar, the electrical leads coupling theinductor portions 120 and 122 to external connections are different toenable all the external connections to be made to the same side of thetransformer assembly 100.

Additionally, the first inductor portion 124 is substantiallysymmetrical with the second inductor portion 126. More specifically, thespiral portion of the first inductor portion 124 has substantially thesame size, shape, and relative orientation as the spiral portion of thesecond inductor portion 126, but is disposed on an opposite side of thesubstrate 102. It should be realized that although the spiral portionsof the first and second inductor portions 124 and 126 are substantiallysimilar, the electrical leads coupling the first and second inductorportions 124 and 126 to external connections are different to enable allthe external connections to be made to the same side of the transformerassembly 100. Therefore, although the first inductor portions 120 and124 are described in detail below, it should be realized that the secondinductor portions 122 and 126 are formed and have substantially the samedimensions and operational characteristics as the first inductorportions 120 and 124.

As shown in FIG. 2, the first inductor portion 120 includes a first end130 and an opposite second end 132. The first end 130 is disposedproximate to a center point 138. The second end 132 is disposed radiallyoutward from the center point 138 proximate to an edge of the substrate102. As shown in FIG. 3, the second inductor portion 122 includes afirst end 134 and an opposite second end 136. The first end 134 isdisposed proximate to the center point 138. The second end 136 isdisposed radially outward from the center point 138 proximate to theedge of the substrate 102.

As shown in FIG. 2, the second inductor portion 124 includes a first end140 and an opposite second end 142. The first end 140 is disposedproximate to the center point 138. The second end 142 is disposedradially outward from the center point 138 proximate to the edge of thesubstrate 102. As shown in FIG. 3, the second inductor portion 126includes a first end 144 and an opposite second end 146. The first end144 is disposed proximate to the center point 138. The second end 146 isdisposed radially outward from the center point 138 proximate to theedge of the substrate 102. In the exemplary embodiment, the first ends130, 134, 140 and 144 are each disposed at an angle with respect to thecenter point 138. More specifically, the first ends 130 and 134 of thefirst spiral inductor 110 are disposed approximately 180 degrees fromthe first ends 140 and 144 of the second spiral inductor 112.

The transformer assembly 100 also includes four mounting pads 150, 152,154 and 156. As shown in FIG. 2, the second end 132 of the firstinductor portion 120 is electrically coupled to the mounting pad 150.Additionally, the second end 142 of the second inductor portion 124 iselectrically coupled to the mounting pad 152 via a pair of capacitorsthat are discussed in more detail below. Referring to FIG. 3, the secondend 136 of the second inductor portion 122 is electrically coupled tothe mounting pad 154 via a pair of capacitors that are discussed in moredetail below. Additionally, the second end 146 of the second inductorportion 126 is electrically coupled to the mounting pad 156.

During assembly, the mounting pads 150, 152, 154 and 156 are utilized tocouple the transformer assembly 100. For example, referring again toFIG. 1, in the exemplary embodiment, the transformer assembly 100 iscoupled between the coil elements 22 and 26. Therefore, each end of thecoil element 22 is coupled to a respective mounting pad 150 and 154.Moreover, each end of the coil element 26 is coupled to a respectivemounting pad 152 and 156 to enable the transformer assembly to becoupled between the coil element 22 and the coil element 26.

Referring again to FIGS. 2 and 3, in the exemplary embodiment, thespiral inductors 110 and 112 each form a planar curve traced by a pointcircling about the center point 138 at an increasing distances from thecenter point 138. Therefore, the spiral inductors 110 and 112 eachincludes a plurality of turns 160 and 162, respectively, that arecoplanar with respect to each other. In the exemplary embodiment, thespiral inductors 110 and 112 have two and a half turns 160 and 162,respectively, wherein each turn spans approximately 360 degrees suchthat an overall length of each of the inductors 110 and 112 isapproximately 900 degrees.

Additionally, the first and second spiral wound inductors 110 and 112form a double spiral arrangement. For example, as shown in FIG. 2, theturns 160 of the first inductor portion 120 are interspersed orinterleaved between the turns 162 of the second inductor portion 124 onthe first surface 104 of the substrate 102. Moreover, as shown in FIG.3, the turns 164 of the first inductor portion 122 are interspersed orinterleaved between the turns 166 of the second inductor portion 126 onthe second surface 106 of the substrate 102. In the exemplaryembodiment, the inductors 110 and 112 each have a substantiallyrectangular cross-sectional profile. Additionally, each of the turns160, 162, 164 and 166 are separated from the other adjacent turns by apredetermined distance. For example, a turn 170 in the first spiralinductor 110 is separated from a turn 172 and a turn 174 in the secondspiral inductor 112 by a gap 176. The size of the gap 176, which may bepredetermined, facilitates electrically isolating the turns from eachother. Moreover, the locations of the two double interleaved spiralinductors 110 and 112, with respect to each other, facilitatesgenerating a relatively strong inductive coupling between the two spiralinductors 110 and 112.

As discussed above, the first and second spiral inductors 110 and 112each have a substantially rectangular shape that represents anArchimedes spiral that may defined as:R _(central)(φ)=R ₀ +s(φ−φ₀)  Equation 1

where:

w is the width of the spiral conductor;

w_(gap) is the width of the gap between the turns;

R₀ is the starting radius of the turns; and

φ₀=π−the starting angle having a slope

$s = {\frac{w + w_{gap}}{2\pi}.}$

The Cartesian coordinates for the spiral inductors 110 and 112 may bedefined as:x _(central)(φ)=R _(central)(φ)cos(φ),y _(central)(φ)=R _(central)(φ)sin(φ).

Referring again to FIGS. 2 and 3, the transformer assembly 100 alsoincludes a plurality of openings 180 that extend through the firstinductor portion 120, the substrate 102, and the second inductor portion122. The transformer assembly 100 also includes a plurality of openings182 that extend through the first inductor portion 124, the substrate102, and the second inductor portion 126. The transformer assembly 100further includes a first pin 184 that is configured to be inserted intoat least one of the openings 180. The transformer assembly 100 alsoincludes a second pin 186 that is configured to be inserted into atleast one of the openings 182. In the exemplary embodiment, the pins 184and 186 are inserted into only one of the openings 180 and 182,respectively, to form a pair of operational inductors 110 and 112respectively, as is discussed in more detail below. The pins 184 and 186are fabricated from a conductive material, such as copper.

The location of the openings 180 and 182 enables the reactance of thetransformer assembly 100 to be adjustable. For example, initially thepin 184 is inserted into an opening 180. Moreover, the pin 186 isinserted into an opening 182. The mutual inductance of the transformerassembly 100 is then measured. To change the mutual inductance of thetransformer assembly 100, the pins 184 and/or 186 may be repositioned toa second different opening until the desired mutual inductance isachieved. In the exemplary embodiment, the pins 184 and 186 arepositioned into a specific opening that creates a mutual inductance thatis substantially equal to a pair of capacitors 190 and 192 that arecoupled to the respective inductor 110 and 112. In the exemplaryembodiment, the capacitors forming the pair of capacitors 190 arecoupled in series. Moreover, the capacitors forming the pair ofcapacitors 192 are coupled in series. Accordingly, the location of thepins 184 and 186 are adjustable such that the inductances of the firstand second inductors 110 and 112 can be chosen within certain limitswhen trying to resonate the transformer assembly 100 with a givencapacitor, such as the pair of capacitors 190 and 192. After, the pins184 and 186 have been positioned in an opening 180 and 182,respectively, the pins 184 and 186 are permanently affixed within theopening. For example, the opposite ends of the pins 184 and 186 aresoldered or brazed to the first and second inductors 110 and 112,respectively.

FIG. 4 is a side view of the inductor 110. It should be realized that tosimplify the explanation of the inductor 110, the inductor 110 is shownas being unfolded, whereas in the exemplary embodiment, the inductor 110is arranged as a spiral as discussed above. As shown in FIG. 4, theinductor 110 includes the first inductor portion 120 mounted on thefirst side 104 of the substrate 102 and the second inductor portion 122mounted on the second side 106 of the substrate 102. The pin 184 isinserted into the opening 180 to couple the first end 130 of the firstinductor portion 120 to the first end 134 of the second inductor portion122 to form an inductor. During operation, current is transmittedthrough the second end 132 of the first inductor portion 120, throughthe first inductor portion 120, through the pin 184, through the secondinductor portion 124, and through the second end 136 of the secondinductor portion 122.

FIG. 5 is a side view of the inductor 112. It should be realized that tosimplify the explanation of the inductor 112, the inductor 112 is shownas being unfolded, whereas in the exemplary embodiment, the inductor 112is arranged as a spiral as discussed above. As shown in FIG. 5, theinductor 112 includes the first inductor portion 124 mounted on thefirst side 104 of the substrate 102 and the second inductor portion 126that is mounted on the second side 106 of the substrate 102. The pin 186is inserted into the opening 182 to couple the first end 140 of thefirst inductor portion 124 to the first end 144 of the second inductorportion 126 to form an inductor. During operation, current istransmitted through the second 142 of the first inductor portion 124,through the first inductor portion 124, through the pin 186, through thesecond inductor portion 126, and exits through the second end 146 of thesecond inductor portion 122.

FIG. 6 is a flowchart of an exemplary method 200 of fabricating atransformer assembly such as the transformer assembly shown in FIGS.1-4. At 202 a first spiral electrical inductor is formed. Morespecifically, at 204 a first inductor portion is formed on a firstsurface of a dielectric substrate. In one embodiment, the first spiralinductor portion may be formed as a separate unit that is affixed to adielectric substrate using, for example, an epoxy. In other embodiments,the first spiral inductor portion is formed on the dielectric substrateusing a chemical vapor deposition procedure. More specifically, thefirst spiral inductor portion is produced by depositing a thin film ofcopper material on the dielectric substrate.

At 206, a second spiral inductor portion is formed on an opposite sideof the dielectric substrate that includes the first spiral inductor.Similar to the first spiral inductor, the second spiral inductor may beformed as a separate unit that is affixed to the dielectric substrate orformed on the dielectric substrate using a chemical vapor depositionprocedure. In the exemplary embodiment, the second spiral inductor isformed to be symmetrical to the first spiral inductor. Morespecifically, the first spiral inductor is substantially the same sizeand has substantially the same shape and relative orientation ofcorresponding turns as the second spiral inductor.

At 208, at least one opening is formed through the first spiralinductor, the second spiral inductor, and the dielectric substrate. Inthe exemplary embodiment, a plurality of openings are formed through thefirst spiral inductor, the second spiral inductor, and the dielectricsubstrate. In the exemplary embodiment, the locations of the openingsare calculated for specified pin positions in radians and inductancevalues. For example, the openings may be located such that each openingproduces a change in inductance of 1 picoFarad (pF). Thus, positioningthe pin in a first opening generates an initial inductance value.Whereas, positioning the pin in a second different opening generates aninductance value that is 1 pF less than the initial inductance value,etc. In this manner, the openings provide incremental adjustments, e.g.1 pF for example, in inductance.

At 210 a second spiral electrical inductor is formed. More specifically,at 212, a first inductor portion is formed on a first surface of adielectric substrate such that the first spiral inductor portion forminga portion of the first spiral inductor is interleaved with the firstspiral inductor portion forming a part of the second spiral inductor.

At 214, a second spiral inductor portion is formed on an opposite sideof the dielectric substrate that includes the first spiral inductor.Similar to the first spiral inductor, the second spiral inductor may beformed as a separate unit that is affixed to the dielectric substrate orformed on the dielectric substrate using a chemical vapor depositionprocedure. In the exemplary embodiment, the second spiral inductor isformed to be symmetrical to the first spiral inductor. Morespecifically, the first spiral inductor is the substantially the samesize and has substantially the same shape and relative orientation ofcorresponding turns as the second spiral inductor.

At 216, at least one opening is formed through the first spiral inductorand a second different pin is inserted into the opening in the secondspiral inductor. As discussed above, a metallic pin is installed in eachof the first and second inductors using, for example, a brazing orsoldering procedure. Optionally, the metallic pins may be secured toboth the first and second inductors using, for example, an epoxymaterial

At 218, a pair of capacitors are coupled to each of the first and secondspiral inductors. During operation, the inductor assemblies describedherein are adjustable to enable the inductor assemblies to be utilizedwith various capacitors. Accordingly, a capacitance value of the pairsof capacitors to be coupled to the inductor assembly to form theresonant circuit may be identified.

Various embodiments of the transformer assembly described herein may beprovided as part of, or used with, a medical imaging system, such asimaging system 300 shown in FIG. 7. It should be appreciated thatalthough the imaging system 300 is illustrated as a single modalityimaging system, the various embodiments may be implemented in or withmulti-modality imaging systems. The imaging system 300 is illustrated asan MRI imaging system and may be combined with different types ofmedical imaging systems, such as a Computed Tomography (CT), PositronEmission Tomography (PET), a Single Photon Emission Computed Tomography(SPECT), as well as an ultrasound system, or any other system capable ofgenerating images, particularly of a human. Moreover, the variousembodiments are not limited to medical imaging systems for imaging humansubjects, but may include veterinary or non-medical systems for imagingnon-human objects, luggage, etc.

Referring to FIG. 7, the imaging system 300 includes an imaging portion302 having an imaging unit 304 (e.g., imaging scanner) and a processingportion 306 that may include a processor 308 or other computing orcontroller device. In particular, the imaging unit 304 enables theimaging system 300 to scan an object or patient 310 to acquire imagedata, which may be image data of all or a portion of the object orpatient 310. The imaging unit 304 includes a gantry 312 having one ormore imaging components (e.g., magnets or magnet windings within thegantry 312) that allow acquisition of the image data. In multi-modalityimaging systems, in addition to the magnet(s) for magnetic resonanceimaging, an x-ray source and detector for computed-tomography imaging,or gamma cameras for nuclear medicine imaging may be provided. Theimaging components produce signals that represent image data that iscommunicated to the processing portion 306 via a communication link 314that may be wired or wireless. During an imaging scan by the imagingunit 304, the gantry 312 and the imaging components mounted thereon ortherein may remain stationary or rotate about or along a center ofrotation defining an examination axis through a bore 316. The patient310 may be positioned within the gantry 312 using, for example, amotorized table 318.

In operation, an output of one or more of the imaging components istransmitted to the processing portion 306, and vice versa, which mayinclude transmitting signals to or from the processor 308 through acontrol interface 320. The processor 308 also may generate controlsignals for controlling the position of the motorized table 318 orimaging components based on user inputs or a predetermined scan. Duringa scan, image data, such as magnetic resonance image data from theimaging components may be communicated to the processor 308 through adata interface 322 via the control interface 320, for example, asacquired by the surface coil 324, illustrated as a torso surface coilarray in FIG. 7.

The processor 308 and associated hardware and software used to acquireand process data may be collectively referred to as a workstation 330.The workstation 330 includes a keyboard 332 and/or other input devicessuch as a mouse, a pointer, and the like, and a monitor 334. The monitor334 displays image data and may accept input from a user if atouchscreen is available.

FIG. 8 is a schematic illustration of the imaging system 300 shown inFIG. 7. In the exemplary embodiment, the imaging system 300 alsoincludes a superconducting magnet 340 formed from magnetic coilssupported on a magnet coil support structure. However, in otherembodiments, different types of magnets may be used, such as permanentmagnets or electromagnets. A vessel 342 (also referred to as a cryostat)surrounds the superconducting magnet 340 and is filled with liquidhelium to cool the coils of the superconducting magnet 340. A thermalinsulation 344 is provided surrounding the outer surface of the vessel342 and the inner surface of the superconducting magnet 340. A pluralityof magnetic gradient coils 346 are provided within the superconductingmagnet 340 and an RF transmit coil 348 is provided within the pluralityof magnetic gradient coils 346. In some embodiments the RF transmit coil348 may be replaced with a transmit and receive coil as described inmore detail herein. The components within the gantry 312 generally formthe imaging portion 302. It should be noted that although thesuperconducting magnet 340 is a cylindrical shaped, other shapes ofmagnets can be used.

The processing portion 306 also generally includes a controller 350, amain magnetic field control 352, a gradient field control 354, a memory356, the display device 334, a transmit-receive (T-R) switch 360, an RFtransmitter 362 and a receiver 364.

In operation, a body of an object, such as the patient 310 (shown inFIG. 14) or a phantom to be imaged, is placed in the bore 316 on asuitable support, for example, the motorized table 318 (shown in FIG.14) or other patient table. The superconducting magnet 340 produces auniform and static main magnetic field B_(o) across the bore 316. Thestrength of the electromagnetic field in the bore 316 andcorrespondingly in the patient 310, is controlled by the controller 350via the main magnetic field control 352, which also controls a supply ofenergizing current to the superconducting magnet 340.

The magnetic gradient coils 346, which include one or more gradient coilelements, are provided so that a magnetic gradient can be imposed on themagnetic field B_(o) in the bore 316 within the superconducting magnet340 in any one or more of three orthogonal directions x, y, and z. Themagnetic gradient coils 346 are energized by the gradient field control354 and are also controlled by the controller 350.

The RF transmit coil 348, which may include a plurality of coils (e.g.,resonant surface coils), is arranged to transmit magnetic pulses and/oroptionally simultaneously detect MR signals from the patient 310 ifreceive coil elements are also provided, such as the surface coil 324(shown in FIG. 14) configured as an RF receive coil. Moreover, thetransformer assembly described herein may be coupled between pairs oftransmit or receive coils as described in FIG. 1. The RF transmit coil348 and the receive surface coil 324 are selectably interconnected toone of the RF transmitter 362 or receiver 364, respectively, by the T-Rswitch 360. The RF transmitter 362 and T-R switch 360 are controlled bythe controller 350 such that RF field pulses or signals are generated bythe RF transmitter 362 and selectively applied to the patient 310 forexcitation of magnetic resonance in the patient 310. In the exemplaryembodiment, any of the inductor assemblies described herein, may beutilized with the RF coils shown in FIG. 8.

Following application of the RF pulses, the T-R switch 360 is againactuated to decouple the RF transmit coil 348 from the RF transmitter362. The detected MR signals are in turn communicated to the controller350. The controller 350 includes a processor (e.g., image reconstructionprocessor), for example, the processor 308 (shown in FIG. 14), thatcontrols the processing of the MR signals to produce signalsrepresentative of an image of the patient 310.

The processed signals representative of the image are also transmittedto the display device 334 to provide a visual display of the image.Specifically, the MR signals fill or form a k-space that is Fouriertransformed to obtain a viewable image. The processed signalsrepresentative of the image are then transmitted to the display device86.

A technical effect of the transformer assembly described herein is toprovide a transformer assembly that includes two double interleavedspiral inductors that are connected through vias to generate relativelystrong inductively coupled inductors. The coupling inductive couplingbetween the pair of spiral inductors may be reduced by connecting thetop and bottom spiral at different locations. The transformer assemblyincludes two pairs of capacitors wherein one pair is coupled to eachrespective spiral inductor. The capacitance of one of the pairs ofcapacitors may be adjusted to cancel the self-inductance of one of thespiral inductors. Moreover, the capacitance of the second pair ofcapacitors may be adjusted to cancel the self-inductance of the secondspiral inductor. The transformer assembly, in the exemplary embodiment,is installed between a pair of RF coils. In the exemplary embodiment,the pins are installed in each respective inductor to achieve a mutualinductance having a negative value. In the exemplary embodiment, thepolarity of the transformer assembly may be reversed by altering thetraces or utilizing jumpers on one side of the transformer assembly.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments without departing from their scope. While the dimensions andtypes of materials described herein are intended to define theparameters of the various embodiments, they are by no means limiting andare merely exemplary. Many other embodiments will be apparent to thoseof skill in the art upon reviewing the above description. The scope ofthe various embodiments should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format and are notintended to be interpreted based on 35 U.S.C. §112, sixth paragraph,unless and until such claim limitations expressly use the phrase “meansfor” followed by a statement of function void of further structure.

This written description uses examples to disclose the variousembodiments, including the best mode, and also to enable any personskilled in the art to practice the various embodiments, including makingand using any devices or systems and performing any incorporatedmethods. The patentable scope of the various embodiments is defined bythe claims, and may include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if the examples have structural elements that do not differfrom the literal language of the claims, or the examples includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

What is claimed is:
 1. A transformer assembly for a magnetic resonanceimaging (MRI) system, said transformer assembly comprising: a substratehaving a first surface and an opposing second surface; a first and asecond spiral wound inductive coils formed on the first surface andforming a first double spiral arrangement such that the first coil isinductively coupled to the second coil; a third and a fourth-spiralwound inductive coils formed on the second surface and forming a seconddouble spiral arrangement such that the third coil is inductivelycoupled to the fourth coil; a plurality of openings extending throughthe first, the second, the third, and the fourth coils; and a pair ofpins being inserted into select ones of the plurality of openingsthrough the first, the second, the third, and the fourth coils to adjusta mutual inductance of the transformer assembly in the MRI system.
 2. Atransformer assembly in accordance with claim 1 wherein the first spiralwound inductive coil is symmetrical with the third spiral woundinductive coil and the second spiral wound inductive coil is symmetricalwith the fourth spiral wound inductive coil.
 3. A transformer assemblyin accordance with claim 1 wherein the first and third-coils areconfigured to be electrically coupled to a first capacitor and thesecond and fourth coils are configured to be electrically coupled to asecond capacitor.
 4. A transformer assembly in accordance with claim 1wherein the first and third coils are configured to be electricallycoupled in series to a respective capacitor, the pins being insertedinto the openings based on the capacitance of the first and secondcapacitors.
 5. A transformer assembly in accordance with claim 1 whereinthe first coil is interleaved with the second coil and the third coil isinterleaved with the fourth coil.
 6. A transformer assembly inaccordance with claim 1 wherein the first coil, the second coil, thethird coil, and the fourth coil each form an Archimedes spiral.
 7. Atransformer assembly in accordance with claim 1 wherein the substrate isfabricated from a dielectric material and the first and second coils arefabricated from a copper material.
 8. A transformer assembly inaccordance with claim 1 wherein the first and second coils include aplurality of turns that are coplanar.
 9. A multiple channel array coilfor a magnetic resonance imaging (MRI) system, comprising: a first radiofrequency (RF) coil; a second RF coil; and a transformer coupled betweenthe first and second coils, the transformer comprising: a substratehaving a first surface and an opposing second surface; a first and asecond spiral wound inductive coils formed on the first surface andforming a double spiral arrangement such that the first coil isinductively coupled to the second coil; a third and a fourth spiralwound inductive coils formed on the second surface and forming a doublespiral arrangement such that the third coil is inductively coupled tothe fourth coil; a plurality of openings extending through the first,the second, the third, and the fourth coils; and a pair of pins beinginserted into selected ones of the plurality of openings through thefirst, the second, the third, and the fourth coils to adjust a mutualinductance of the transformer assembly in the MRI system.
 10. An arraycoil in accordance with claim 9 wherein the first and third spiral woundinductive coils are configured to be electrically coupled to a firstcapacitor and the second and fourth spiral wound inductive coils areelectrically coupled to a second capacitor.
 11. An array coil inaccordance with claim 9 wherein the first and third-coils areelectrically coupled in series to a first capacitor and the second andfourth coils are electrically coupled to a second capacitor, the pinsbeing inserted into the openings based on the capacitance of the firstand second capacitors.
 12. An array coil in accordance with claim 9wherein the first coil is interleaved with the second coil and the thirdcoil is interleaved with the fourth coil.
 13. An array coil inaccordance with claim 9 wherein the first coil, the second coil, thethird coil, and the fourth coil each form an Archimedes spiral.
 14. Anarray coil in accordance with claim 9 the substrate is fabricated from adielectric material and the first and second coils are fabricated from acopper material.
 15. A transformer assembly in accordance with claim 9wherein the first and second coils include a plurality of turns that arecoplanar.
 16. An array coil in accordance with claim 9 wherein the firstRF coil and the second RF coil comprise surface coils.
 17. A method offabricating a transformer assembly for a magnetic resonance imaging(MRI), said method comprising: forming a first spiral inductor and asecond spiral inductor on a first surface of a dielectric such that thefirst spiral inductor is interleaved with the second spiral inductor;forming a third-spiral inductor and a fourth spiral inductor on thesecond surface of the substrate such that the third spiral inductor isinterleaved with the fourth spiral inductor; forming a plurality ofopenings through the first, the second, the third, and the fourth coils;and inserting a pair of pins into selected ones of the plurality ofopenings through the first, the second, the third, and the fourth coilsto adjust a mutual inductance of the transformer assembly in the MRIsystem.
 18. The method of claim 17, wherein the first and third coilsare electrically coupled in series to a first capacitor and the secondand fourth coils are electrically coupled to a second capacitor, saidmethod further comprising inserting the pins into the openings based onthe capacitance of the first and second capacitors.
 19. The method ofclaim 17, wherein the first coil is interleaved with the second coil andthe third coil is interleaved with the fourth coil.